this is no longer going to be "his" = in his room I need a monitor
Frankly, kids should not have computers in their rooms anyway. Despite what every kid thinks, they are not invincible, they don't know everything, and it can happen to them. Kids will download tunes and videos from anywhere they can get them for free. These are the very type files and places badguys frequent to launch their malware and to seek out and stalk their next targets/victims. Kids are frequent targets of cyberbullies at social networking sites. Because kids don't "practice safe computing" these computers are frequently infected by badguys. As such, these computers become a threat to them, and in turn your network and therefore your computers, and you.
Badguys will use these computers to steal identities, bank account numbers and passwords. Predators will use them to seek out their next victims to cause bodily harm, or worse.
While you may totally trust your child, peer pressure often dictates their behavior (5 kids and 8 grandkids - I know). This is especially true if they are allowed to have "friends" in their room, behind closed doors. Can you trust all their friends?
Kids' computers should be located in a central location where parents can see what they are doing. Will the kids hate you for it? Probably. Oh well! Life isn't fair!
And kids should never have administrator accounts either, or the passwords to your accounts. And of course, you need to ensure their computers are kept fully updated, behind a firewall, and have a good anti-malware solution in place at all times too.